Here's another archival post of mine.
Suasion. I remember this word raising my hackles a couple of years ago when it was the wotd on DD. Merriam-Webster defines both "suasion" and "persuasion" as "the act of persuading". Now, normally, I would reiterate that there are no true synonyms and distinguish the etymologies on each, except the etymologies are a little fuzzy. Suasion says it comes from Latin "suadere" for "persuasion" or "to advise", while persuasion says it comes from--wait for it--"per" and "suasion",so these are unhelpful. The mere addition of the "per" meaning through, doesn't add anything to the etymology or the meaning. Persuasion does not really mean through suasion, because the definition of suasion is backward to that construction. Suasion means through persuasion and therefore should actually be "perpersuasion" (Or do the “per”s cancel?) So, I think we have an issue of lazy usage being justified retroactively, since these words both originated in the late Middle Ages, c. 1380. But, I'll make one last stab at a distinction, just for old times sake. The usage of suasion from the examples from DD is non-specific, to a general perspective (e.g., moral or cultural norms), while persuasion is for a definite idea or opinion. I regularly persuade the judge to my argument, or try to persuade people to order different things off the menu so we can share and sample, but I might try to suade a child to be kind to animals or to always say please and thank you. Still not much use for suasion. Perhaps suasion is just insipid.